1. Field of the Invention
The present invention relates to a hard coating that is to be disposed on a surface of a body of such as a machining tool, especially, to the art of disposing an outer layer on a diamond layer by the PVD method.
2. Description of Related Art
A diamond-coated tool coated with a diamond coating on the body made of such as cemented carbide is suggested for a cutting tool such as an end mill, a turning tool, a tap, a drill or other tools. JP 2519037B and JP 2002-79406A disclose examples of such tools. Although these diamond-coated tools have very high hardness, superior wear resistance and adhesion resistance, they often does not offer sufficiently high performance in cutting of the composite material including a material of iron series or in cutting of a material with its cutting point at a high temperature due to their low oxidation resistance. Then such as JP 2003-145309A discloses an art to coat a diamond coating with an outer layer including an intermetallic compound of such as TiAlN by such as the PVD (physical vapor deposition) method. JP 2004-193522A and JP 10-146703A disclose an art of doping with boron (B) upon the crystal growth of the diamond by such as the microwave plasma CVD (chemical vapor deposition) method in order to let it have electrical conductivity and to improve it in oxidation resistance.
Doping with boron for the diamond coating disposed on the surface of such as a machining tool body, however, has not been suggested yet. Substantial insulation of diamond itself causes low strength of adhesion as a result of insufficient electrical conductivity characteristics from the early period of the coating process upon disposing an outer layer of such as TiAlN on the diamond coating by the PVD method, and causes insufficient durability as a result of flaking or removal of the outer layer in the early period of cutting.
It is therefore an object of the present invention to provide a hard coating with superior durability by improving the strength of adhesion of the outer layer to the diamond layer by the PVD method.